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how many wheels do you need? Just two? Do they have to be 100% straight?

You could try asking around your local bike shops, quite often when they replace peoples wheels they just chuck the old ones away. If you only need the rims it doesn't matter if the hubs and spokes are knackered.

Here's my slightly rickety sieve. I guess you wanted to leave the mouth of the drum quite open, hence the need for castors, but I found this arrangement to be good enough. I was sieving gravel with some soil in it - if it is more soil than gravel then it would need to be dryish in order not to bung up the mesh.

All of this is giving me flash backs to a time when I worked for a recycling company and ran one of these. If they stuck too much wet soil in the hopper the trommel would get bunged up and you'd have to dig it out with a shovel. Not much fun. Especially when it was big enough to stand in but only at a crouch.

Here's my slightly rickety sieve. I guess you wanted to leave the mouth of the drum quite open, hence the need for castors, but I found this arrangement to be good enough. I was sieving gravel with some soil in it - if it is more soil than gravel then it would need to be dryish in order not to bung up the mesh.

Looks really good. Unfortunately I don't have a welder, so my options are a bit more limited...that's why I'm going for castors round the outer edge of the rims, held inside a wooden frame.

Luckily, even after the recent downpours, my soil is pretty dryish. Living near the top of a hill with gravelly soil does tend to help the drainage!

All of this is giving me flash backs to a time when I worked for a recycling company and ran one of these. If they stuck too much wet soil in the hopper the trommel would get bunged up and you'd have to dig it out with a shovel. Not much fun. Especially when it was big enough to stand in but only at a crouch.

I don't miss that job.

Sounds horrendous... glad mine is on a slightly smaller scale / won't have a hopper!

Have finally managed to get round to building the rotary sieve/ trommel after well over a year of scavenging bits/pieces and tripping over them.

It's great! Even better, my kids love it so they spent much of today loading in the big pile of soil, just calling on me when the wheelbarrows needed emptying.Raised beds in the flower garden filled today and the veg patch should be up/running by the end of the week...Even SWMBO is impressed!

A few hints for anyone else who might be thinking about making a rotary sieve:

1. Make sure all your wheel rims are roughly the same size. It’s theoretically possible to have a cone shaped drum, but it’s much harder to get it aligned and working reliably.

2. Use mountain bike rims. They’re wider than racing bike rims. Unless you use tiny castors, most castors are too wide to slot inside mountain bike rims and it’s a lot of hassle to cut/file them down. I ended up throwing away some 700c racing bike rims and buying some 26” mountain bike rims because it was easier then messing about with the castors

3. The earlier you start collecting bike rims, the cheaper it will be. If you can’t find any free ones, look on ebay for 99p “spares or repairs” bikes, or in the recycling bit of your local waste site. It can be cheaper to buy a whole bike and throw away the frame. My first set of wheels was free. My 2nd set cost 99p for the whole bike. When I decided at the last minute that I needed a 3rd set that matched, they cost £10.50 but I could pick them up the same day...

4. Most weldmesh comes in 36” width and this is plenty if you have sandy soil. I used 48” mesh because I had some, but most soil falls through the sieve in the first 18” so the extra 12” just makes my device less portable.

5. If you use 36” mesh, I reckon you’d get away with just 3 bike wheels (18” apart). I used 4 wheels on my 48” mesh, so they are 16” apart.

6. 10-12mm mesh gives a lovely fine material.

7. Make sure you’ve got plenty of cable ties – it takes more than you think to fix the mesh. 140mm ties aren’t quite long enough to form a loop through 2 adjacent spoke holes – I used about 130 cable ties (200mm long). A pack of 100 should be enough if you’re using 36” mesh and only 3 wheels.

8. 200mm cable ties are usually 4.5 or 4.8mm wide, but these are a tight fit through the spoke holes, so worth running a 5mm drill though each hole to make your life easier

9. If your arms aren’t long enough to reach the inside of the middle of the drum (less likely if your drum is only 36” long) then persuade a small child to stand still. Lower the drum down over their head, and they can help to push the cable ties back to you.

10. Tumble dryer motors are easier to use than washing machine motors – they are designed to go at a slower speed so you probably won’t need to worry about speed control or extra gearing/pulleys. If you’re scavenging a motor, get the belt, too. Don’t forget the capacitor for the motor.

11. Do put at least two castors (one at each end) over the top of the drum, to stop it lifting off the lower castors/ to keep the belt tight, but think about how you will be able to remove these castors easily later if you need to get the drum out.

12. Use the flat drive belts (like on tumble dryers) rather than a v-belt – they’re better at gripping the outside of the wheel rim.

13. Remember to mount the motor on top of the sieve, not underneath (where it will get full of dirt!)

14. Think about how you will cope when the belt stretches. I just mounted the motor on a big bit of wood that was attached to the main frame with 2 long screws. As the belt stretched slightly in the first hour, I loosened the big screws and put packing pieces underneath

15. Think about electrical safety and stopping the motor if something jams. I used a waterproof light switch (motor is only 1.2A and the light switch is rated at 10A, so even if there’s a bit of surge on startup, it should be fine). Don’t be tempted to rely on pulling the plug out of the extension lead quickly enough. Do connect an earth wire to the motor case. Make sure connections are insulated.

16. Think about how you’ll keep the motor/electrics dry if it rains and you can't be bothered/don't have space to lug the device inside. I used a small tarpaulin, with a bit of bungee cord on each corner to clip onto the 4 screw hooks placed strategically.

17. Make sure the legs are long enough so you can fit your wheelbarrow underneath, but keep the height as low as possible since you’ll have to lift all the soil up to it…

18. A bit of difference in the dampness of the soil makes a big difference to how well it will sieve. Damp soil is noticeably heavier, so it’s harder work for you and the motor. It also sticks together, so you get more lumps of soil going all the way through. If you've got a big pile to sieve, do a bit off the top, then stop for a cuppa/afternoon nap while the next bit dries out.

19. If you don't have a friend, think about sticking a couple of big wheels on the feet on one end of the device, to make it easier to move around. It's not easy to move it alone.

20. Stick a bit of board over the frame at the loading end, and cut out a circle to expose the open end of the drum. When you misdirect a shovel full of soil, it bounces off the board instead of polluting your nice sieved soil in the wheelbarrow. I used a bit of ancient plywood, but I reckon even corrugated cardboard would work (until it got wet). This board also has the advantage that it keeps you away from the potentially sharp rotating edges on the end of the drum.

21. A slope of 4" vertically over 48" horizontally seems about right. It could go slightly steeper

I know it's been a while since this discussion, but I chanced upon an alternative way of making a trommel that would suit the handyman/gardener. If you own a small concrete mixer and can get a spare drum from a knackered one, this may be just the job for a spring project: